In recent years, considerable effort has been directed toward the protection of workers from the high noise levels generated by industrial machines. When high speed machinery, such as sewing machines, is involved, noise reduction activities have been focused in two major areas. The first area of activity is in the redesign and engineering of the machines themselves to eliminate the noise at its source. However, the inherent nature of high speed sewing machines and the economics of redesign place limitations upon the practical potential of sufficiently reducing sewing machine noise levels. Furthermore, many existing machines have undesirably high operating noise levels. Modification of these existing machines for reducing the noise to an acceptable level is highly impractical, and in many cases, impossible. Hence, considerable activity has been focused upon the development of noise attenuation structures for acoustically shielding and insulating the noise from a worker an example of such a structure is disclosed in Applicant's U.S. Pat. No. 4,509,442.
The design of acoustical shields for insulating workers from noise generated by industrial sewing machines has been complicated by several factors. One of the complicating factors is the need for access to the working components of the machine. In this regard, access to the thread track is of particular importance. Such access is needed not only for maintenance and repair, but also for routine operational procedures. Unfortunately, acoustical shields inherently tend to interfere with the required access to the sewing machine. For example, many prior art designs require cumbersome disassembly and reassembly of the acoustical shield to gain access to the machine.
A further complicating factor in acoustical shield design for sewing machines is the need to freely feed thread to the sewing machine from a source outside the acoustical shield. Prior acoustical shield designs for sewing machines or the like have tended to either interfere with the thread feed from an external source or have left substantial voids in the acoustical shield itself, which voids have substantially and adversely effected the efficiency of the acoustical shield assembly. In U.S. Pat. No. 4,074,725 to Bader et al, for example, a multicomponent hinged cover for attenuating noise generated by selective components of a weaving machine is disclosed. However, the noise attenuating cover disclosed in this mentioned patent does not even attempt to attenuate noise escaping from the machine about the thread intake.